Reforming of hydrocarbon fuels to make hydrogen is well known in the art. Conventionally, hydrocarbons are reformed predominately in large-scale industrial facilities providing hydrogen for bulk storage and redistribution, or producing hydrogen as an on-line, upstream reagent for another large-scale chemical process. For the most part, these prior processes operate continuously and at steady-state conditions.
More recently, however, a strong interest has developed in providing hydrocarbon-reforming reactors integrated with an end use of the hydrogen. Also, there is a strong interest to develop a low-cost, small-scale source for hydrogen that can replace the need for storing hydrogen gas on site or on board. More particularly, a great interest has developed in providing reactors for producing hydrogen, which can be integrated with a fuel cell which uses hydrogen as a fuel source to generate electricity. Such hydrogen generator/fuel cell systems are being pursued for stationary uses such as providing electrical power to a stationary facility (home or business), for portable electric power uses, and for transportation.
In mobile applications such as a vehicle, or in any “power on demand” system, such as a backup electric power supply, the system must run these reactions continuously at variable demands for total hydrogen production. In addition, the system must be inexpensive and easy to assemble and maintain. In effect, it must cost and act more like an automobile engine, and less like a small chemical plant.
Reactions used to generate hydrogen enriched gas from hydrocarbons, including those for treating such product gases to increase the hydrogen concentration or reduce carbon monoxide include partial oxidation (with or without a catalyst), steam reforming, water gas shift reactions, and selective or preferential oxidation. Of these, only steam reforming is not exothermic. Hence to increase or optimize an integrated reactor's efficiency the heat generated by any of the exothermic reactions needs to be used for useful work, such as for preheating reactants or reactions. One example is to use the heat from partial oxidation to drive a steam reforming reaction, to provide autothermal reforming “ATR.”
Also, it is common to control temperatures of exothermic reactions by heat transfer to a cooling heat transfer medium.
In some reactors, particularly reactors providing steam reforming, auxiliary heat provided by a burner may be desirable or necessary to drive the steam reforming. Even with reactors employing ATR may benefit from an auxiliary burner to enhance performance during start up or transient load conditions. Additionally, burners are commonly used to burn the anode gas from a fuel cell.
In addition, if such a reactor is integrated with a fuel cell, by product heat from the fuel cell must also be used efficiently.
The plumbing conventionally employed to accomplish all of the heat transfers necessary, available, or desirable in an integrated reactor or integrated reactor and fuel cell (including coiled tubes, fins, tube clusters, pool boilers, and detached heat exchangers) can be difficult to assemble and maintain, and increase the cost and size of an integrated unit.
The present invention addresses the above short comings in the art provides other advantages as will be understood by those in the art in view of the following specification and claims.